PSI - Issue 28

Fatih Kocatürk et al. / Procedia Structural Integrity 28 (2020) 1276–1285 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. Schematic of bolt having shaft diameter greater than the socket diameter.

2. Sample specification In this study, M8 bolt with 1,25 thread pitch and 23 mm shaft length was chosen as the representative sample. Bolt with N10 socket form and satisfying the mechanical requirements for 8.8 grade as given in (ISO 898-1, 2004) was modelled by using Simufact.forming finite element software. The material was 23MnB4, i.e. one of the most widely preferred low alloy steel in cold forging. 3. Socket depth estimation for bolts having shaft diameter smaller than socket diameter 3.1. Analytical modelling Analytical Modelling studies were initiated by investigating Eq. (1) in detail, which is valid for the case of bolts having shaft diameter greater than the socket diameter. The minimum distance between the end of the socket and the bottom of the head, ��� , can be found in Eq. (1). The ��� value is called as the residual floor thickness and measured with the relation ��� � � for an inbus bolt where the head height is and the socket depth is shown in Fig. 2. When the shaft diameter is greater than the socket diameter, the fracture pattern is expected to be formed between the bottom of head and the end of the socket (see Fig. 1). However, when the shaft diameter is smaller than the socket diameter, the fracture pattern was formed between the bottom of head and a point , which is located between the end of the socket and the tip of the socket based on the experiences in production (see Fig. 2). The two-dimensional bolt cross section is shown in Fig. 3 to locate the break point, � , required to calculate the surface area of the fracture cone. The local origin of the cross sectional area, �0,0� is selected as shown in Fig. 4. Then, � � ��, �� is obtained as follows: Let us call the line passing through � and � as � and the line passing through � and � as � .  First, the equation of the line � is found by using the slope of the line, � � ��� � , and the point � � � � � � , ��� � �� in Eq. (3). The equation of a line can be found given that a point, � � �� � , � � , on the line and its slope, , is known by using Eq. (2).